1. Technical Field of the Invention
The present invention relates to a display of characteristic values (such as frequency, phase, and level) of a signal while the characteristic values are associated with time.
2. Related Art
A spectrum analyzer which measures a change in frequency of a signal with respect to time has conventionally been known (refer to Abstract of a patent document 1 (Japanese Patent Application Laid-open No. Hei 11-118848)).
On this occasion, a case in which a signal repeats ON/OFF is considerable. FIG. 9 is a diagram showing a conventional example showing the frequency of a signal with respect to time in the case in which the signal repeats ON/OFF. The frequency of a noise is shown in a period in which the signal is OFF (absent), and the frequency of the signal is shown in a period in which the signal is ON (present). It is generally often the case that the frequency of the signal is to be measured, and the frequency of the noise is not to be measured.